1. Field of the Invention
This invention relates to the development of a vaccine against Theileria parva, which is a protozoan parasite infecting cattle in Africa. The invention specifically relates to the use of the 67 kDa glycoprotein from the surface of the T. parva sporozoite as an immunogen for inducing immunoprotection against T. parva in bovine species. This 67 kDa antigen is produced using recombinant genetics. Plasmids containing nucleic acid segments encoding the antigen, host cells containing the nucleic acid segments and recombinant methods for producing the antigen are part of this invention.
This invention also relates to the development of live vaccines against Theileria parva, which is a protozoan parasite infecting cattle in Africa. The invention specifically relates to the use of live attenuated strains of Salmonella typhimurium and vaccinia virus carrying the gene encoding the 67 kDa glycoprotein from the surface of the T. parva sporozoite as an immunogen for inducing immunoprotection against T. parva in bovine species. Construction of attenuated S. typhimurium, vaccinia viruses and plasmids containing nucleic acid segments encoding the antigen are a part of this invention. Finally this invention provides methods for immunoprotecting animals against T. parva infection.
The protozoan parasite, Theileria parva, which is transmitted by the ixodid tick, Rhipicephalus appendiculatus, causes East Coast fever (ECF), a disease of cattle which continues to exert severe limitations on the development of the livestock industry in much of Eastern and Central Africa. T. parva is divided into three sub-types, T. parva parva, T. parva bovis and T. parva lawrencei. This classification is based on certain epidemiological and behavioral characteristics of the parasites. T. parva lawrencei originates from buffalo and is highly pathogenic to cattle. T. parva bovis and T. parva parva are maintained between cattle and differ in pathogenicity. Despite this classification there is no definitive proof for sub-speciation of T. parva. For the purposes of this document, T. parva therefore encompasses all three sub-types which are themselves heterogenous in nature.
Infection with T. parva is initiated when sporozoites are inoculated into the mammalian hosts by the tick during feeding. The sporozoites enter lymphocytes where they mature into schizonts. The intralymphocytic schizonts later develop to merozoites which enter erythrocytes to become piroplasms which are ingested by ticks feeding on the parasitized host. Gametes which develop from the piroplasms fuse to initiate the parasite life cycle in the tick which culminates in the production of sporozoites in the tick salivary gland.